There is an ever-increasing need for electronic devices and systems having improved reliability. One potential source of failure for an electronic system is its cooling system. The electronic components of such systems typically generate a considerable amount of heat in an enclosed or semi-enclosed space. It is often necessary to provide a cooling system in order to prevent temperature gradients that could compromise the function of such electronic components.
One method of cooling is the use of an air mover such as a fan or impeller in order to establish air flow across the electronic components. Such air flow facilitates the dissipation of generated heat by convection heat transfer. In some cooling systems, multiple air movers are mounted in a bank arrangement wherein each of the air movers moves a portion of the air that is being used to cool the electronic system, and the air movers in combination provide the cooling capacity necessary to cool the electronic system.
Multiple air movers are sometimes mounted to move air along air flow paths that are arranged in a parallel orientation. This is not to say that the air flow paths are arranged parallel with respect to one another in the geometric sense; instead, such parallel orientation refers to the movement by each of the air movers of a separable portion of the air flow so that the combined effort of the air movers is sufficient to generate a total air flow requirement for suitable heat transfer.
It has been discovered, however, that the failure of one or more air movers in a system having multiple air movers can change the air-flow pattern in a manner that compromises the dissipation of heat generated by the electronic system. For purposes of illustration, FIGS. 1 and 2 show schematic representations of examples of air moving systems that include multiple air movers.
Referring first to FIG. 1, an air moving system (generally designated by the numeral "10") is intended to dissipate heat that is generated within an enclosure 12 such as a cabinet, chassis, housing or other structure. The enclosure 12 has an interior 14 in which an electronic system can be mounted. Enclosure 12 also has one or more openings such as an opening 16 for intake air flow as well as a pair of openings 18a and 18b for exhaust air flow. Air movers (not shown) are oriented to urge air flow through opening 16, into interior 14, and out to the exterior of enclosure 12 through openings 18a and 18b. More specifically, intake air flow "A" is urged into opening 16 and exhaust air flow "B.sub.1 " and "B.sub.2 " is urged outwardly through openings 18a and 18b, respectively. Air is therefore caused to flow along primary air flow paths 20a and 20b, which are shown in FIG. 1 as dotted lines extending from opening 16 to openings 18a and 18b.
Although not shown in FIG. 1, it will be understood that an air mover is positioned anywhere along each of the primary air flow paths 20a and 20b in order to urge air flow along the respective paths. For example, an air mover can be positioned within interior 14 proximal to each opening 18a and 18b, near opening 16, or anywhere in the space between opening 16 and 18a or 18b. These air movers cooperate to generate intake air flow A by producing a low pressure zone within interior 14 of enclosure 12, thereby drawing air into the enclosure and then forcing air outwardly in the form of exhaust air flow B.sub.1 and B.sub.2.
It has been discovered that the failure of an air mover can result in reverse air flow through the exhaust openings and that such reverse air flow can change the air flow pattern detrimentally and reduce the cooling air flow that is directed across the heat-generating components of the electronic system. For example, if an air mover positioned along primary air flow path 20a fails, exhaust air flow B.sub.1 will be replaced by reverse air flow "C.sub.1 " through opening 18a due to the low pressure zone within interior 14. Similarly, failure of an air mover oriented along primary air flow path 20b would result in the replacement of exhaust air flow B.sub.2 with reverse air flow "C.sub.2 " through opening 18b. A failure of an air mover oriented along primary air flow paths 20a or 20b would therefore tend to result in air flow along a secondary air flow path 20c between openings 18a and 18b. For example, if an air mover positioned along primary air flow path 20a were to fail, then reverse air flow C.sub.1 through opening 18a would travel along secondary air flow path 20c to opening 18b. Such a change in the air flow pattern reduces the flow of air across the heat-generating electronic components and also re-directs air flow away from portions of the interior 14 of enclosure 12.
Referring now to FIG. 2, an air mover system 30 also includes an enclosure 32 with an interior 34, as well as openings 36 for exhaust air flow and 38a and 38b for intake air flow. The air mover system 30 in FIG. 2 differs from the one illustrated in FIG. 1 because it is adapted for the use of air movers (not shown) that are positioned proximal to openings 38a and 38b to urge intake air flow A.sub.1 and A.sub.2 into interior 34 and out from interior 34 as exhaust air flow B by creating a high pressure zone within interior 34. Accordingly, air movers positioned along primary air flow paths 40a and 40b urge air through the interior 34 from openings 38a and 38b to opening 36. Failure of an air mover therefore would result in reverse air flow C.sub.1 or C.sub.2 as well as air flow along a secondary air flow path 40c.
As illustrated in FIGS. 1 and 2, it has been discovered that the failure of an air mover in an air moving system that utilizes multiple air movers can compromise the cooling effect significantly. Not only does such a failure reduce the intake and exhaust air flow by eliminating the contribution of the failed air mover, but such a failure also results in a detrimental change in the air flow pattern and air flow rate within the enclosure from which heat is being dissipated.
Attempts have been made in the past in order to overcome this problem. For example, U.S. Pat. No. 5,438,226, issued to Douglas A. Kuchta, describes the use of louvers that can be added to a fan assembly in order to prevent backwards flow of air through the opening of a failed fan. The Kuchta patent also discloses the arrangement of air movers in series with respect to the air flow as opposed to banked designs which arrange fans in parallel with the air flow. The series air moving system proposed by the Kuchta patent is intended to reduce hot spots which may result when one fan in a parallel fan bank fails and to reduce backward air flow through a failing air mover because the remaining air mover in series establishes flow in the proper direction.
Nevertheless, there remains a need for an improved air mover system that is capable of reducing reverse air flow in the event that one or more of multiple air movers fails.